Fueling system vapor recovery and containment performance monitor and method of operation thereof

ABSTRACT

A method and apparatus for monitoring and determining fuel vapor recovery performance is disclosed. The dispensing of liquid fuel into a tank by a conventional gas pump nozzle naturally displaces a mixture of air and fuel ullage vapor in the tank. These displaced vapors may be recovered at the dispensing point nozzle by a vapor recovery system. A properly functioning vapor recovery system recovers approximately one unit volume of vapor for every unit volume of dispensed liquid fuel. The ratio of recovered vapor to dispensed fuel is termed the A/L ratio, which should ideally be approximately equal to one (1). The A/L ratio, and thus the proper functioning of the vapor recovery system, may be determined by measuring liquid fuel flow and return vapor flow (using a vapor flow sensor) on a nozzle-by-nozzle basis. The disclosed methods and apparatus provide for the determination of A/L ratios for individual nozzles using a reduced number of vapor flow sensors. The disclosed methods and apparatus also provide for the determination of fuel dispensing system vapor containment integrity, and the differentiation of true vapor recovery failures as opposed to false failures resulting from the refueling of vehicles provided with onboard vapor recovery systems.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The application relates to and claims priority on U.S.Provisional Patent Application Ser. No. 60/168,029, filed on Nov. 30,1999, entitled “Fueling System Vapor Recovery Performance Monitor,” onU.S. Provisional Patent Application Ser. No. 60/202,054, filed on May 5,2000, entitled “Fueling System Vapor Recovery Performance Monitor,” andon U.S. Provisional Patent Application Ser. No. 60/202,659, filed on May8, 2000, entitled “Method of Determining Failure of Fuel Vapor RecoverySystem.”

FIELD OF THE INVENTION

[0002] The present invention relates to a vapor recovery performancemonitor for use in connection with gasoline dispensing facilities.

BACKGROUND OF THE INVENTION

[0003] Gasoline dispensing facilities (i.e. gasoline stations) oftensuffer from a loss of fuel to the atmosphere due to inadequate vaporcollection during fuel dispensing activities, excess liquid fuelevaporation in the containment tank system, and inadequate reclamationof the vapors during tanker truck deliveries. Lost vapor is an airpollution problem which is monitored and regulated by both the federalgovernment and state governments. Attempts to minimize losses to theatmosphere have been effected by various vapor recovery methods. Suchmethods include: “Stage-I vapor recovery” where vapors are returned fromthe underground fuel storage tank to the delivery truck; “Stage-II vaporrecovery” where vapors are returned from the refueled vehicle tank tothe underground storage tank; vapor processing where the fuel/air vapormix from the underground storage tank is received and the vapor isliquefied and returned as liquid fuel to the underground storage tank;burning excess vapor off and venting the less polluting combustionproducts to the atmosphere; and other fuel/air mix separation methods.

[0004] A “balance” Stage-II Vapor Recovery System (VRS) may make use ofa dispensing nozzle bellows seal to the vehicle tank filler pipeopening. This seal provides an enclosed space between the vehicle tankand the VRS. During fuel dispensing, the liquid fuel entering thevehicle tank creates a positive pressure which pushes out the ullagespace vapors through the bellows sealed area into the nozzle vaporreturn port, through the dispensing nozzle and hose paths, and on intothe VRS.

[0005] It has been found that even with these measures, substantialamounts of hydrocarbon vapors are lost to the atmosphere, often due topoor equipment reliability and inadequate maintenance. This isespecially true with Stage-II systems. One way to reduce this problem isto provide a vapor recovery system monitoring data acquisition andanalysis system to provide notification when the system is not workingas required. Such monitoring systems may be especially applicable toStage-II systems.

[0006] When working properly, Stage-II vapor recovery results in equalexchanges of air or vapor (A) and liquid (L) between the main fuelstorage tank and the consumer's gas tank. Ideally, Stage-II vaporrecovery produces an A/L ratio very close to 1. In other words, returnedvapor replaces an equal amount of liquid in the main fuel storage tankduring refueling transactions. When the A/L ratio is close to 1,refueling vapors are collected, the ingress of fresh air into thestorage tank is minimized and the accumulation of an excess of positiveor negative pressure in the main fuel storage tank is prevented. Thisminimizes losses at the dispensing nozzle and evaporation and leakage ofexcess vapors from the containment storage tank. Measurement of the A/Lratio thus provides an indication of proper Stage-II vapor collectionoperation. A low ratio means that vapor is not moving properly throughthe dispensing nozzle, hose, or other part of the system back to thestorage tank, possibly due to an obstruction or defective component.

[0007] Recently, the Califormia Air Resources Board (CARB) has beenproducing new requirements for Enhanced Vapor Recovery (EVR) equipment.These include stringent vapor recovery system monitoring and In-StationDiagnostics (ISD) requirements to continuously determine whether or notthe systems are working properly. CARB has proposed that, when the A/Lratio drops below a prescribed limit for a single or some sequence offueling transactions, an alarm be issued and the underground storagetank pump be disabled to allow repair to prevent further significantvapor losses. The proposed regulations also specify an elaborate andexpensive monitoring system with many sensors which will be difficult towire to a common data acquisition system.

[0008] The CARB proposal requires that Air-to-Liquid (A/L) volume ratiosensors be installed at each dispensing hose or fuel dispensing pointand pressure sensors be installed to measure the main fuel storage tankvapor space pressure. Note that the term ‘Air’ is used loosely here torefer to the air-vapor mix being returned from the refueled vehicle tankto the Underground storage tank. The sensors would be wired to a commondata acquisition system used for data logging, storage, and limitedpass/fail analysis. It is likely that such sensors would comprise AirFlow Sensors (AFS's).

[0009] A first embodiment of the present invention provides a morepractical and less expensive solution than that proposed by CARB, whichcan substantially provide the monitoring capabilities needed. In thisfirst embodiment of the present invention, the multiple AFS's called forby the CARB proposal may be replaced by fewer, or only one, AFS inconjunction with a more sophisticated AFS data analysis method.

[0010] With respect to use of vapor pressure sensors, CARB also proposesthat these sensors be used to passively monitor the level of pressure inthe main fuel storage tank vapor space, which is common to the fuelingfacility, to not only provide indication of proper operation of Stage-IIvapor recovery methods, but also system containment integrity. This isdone by monitoring the pressure patterns that occur within the storagetank during the various phases of storage tank and dispenser operation.The complexity of these patterns is a function of the type of Stage-IIsystem in use.

[0011] CARB has proposed putting constraints on the pressure versus timerelationships to identify when the vapor recovery system is causingundesirably high pressures for long enough time periods. when the vaporrecovery system produces these elevated pressures, it may forcesignificant amounts of vapor past the pressure relief valve at the endof the storage tank vent pipe or out of other leaky system valves andfittings and into the atmosphere as air pollution.

[0012] CARB proposes a passive test for identifying elevated storagetank pressures. The purpose of the passive test is to determine whethervapors are being properly retained in the storage tank vapor space. Thisis done by continuously monitoring and watching for evidence of anon-tight or improperly operated vapor recovery components by trackingsmall pressure levels over time and comparing them to prescribedoperating requirements.

[0013] For instance, for a vapor recovery system that is intended tocontinuously maintain negative storage tank vapor space pressures, theCARB proposed requirements were (at one time) that an error conditionwould exist when pressure exceeds (i.e. is higher than)-0.1 inch watercolumn (w.c.) for either more than one (1) consecutive hour, or morethan 3 hours in any 24 hour period. An error condition would also existwhen pressure exceeds (i.e. is higher than)+0.25 inches w.c. for eithermore than one (1) consecutive hour, or more than 3 hours in any 24 hourperiod. An error condition would also exist if pressure exceeded +1.0inches w.c. for more than 1 hour in any 24 hour period. Determination ofthe foregoing error conditions requires frequent pressure measurements,data storage, and analysis. CARB has struggled with these requirementsfor a passive-type test and has changed them more than once.

[0014] In a second embodiment of the invention the CARB proposed passivepressure monitoring test may be augmented or replaced with an activepressure “tightness” or “leakage” test which provides a more definitiveindication of system containment integrity. The active tightness testmay only need to be run occasionally to find a break in the system. Aonce a day or once a month test is consistent with the intent of thevariously proposed CARB test pass/fail criteria.

[0015] In yet another embodiment of the invention, the CARB proposedpassive test for leakage may be replaced with an improved passive testfor vapor leakage. Instead of measuring absolute pressure in the vaporcontaining elements of a facility, in the improved test changes inpressure over time are used to determine whether vapors are leaking fromthe system.

[0016] Both the aforementioned CARB methods for determining vaporrecovery system performance and those of the invention may bedetrimentally effected by the introduction of vehicles with OnboardRefueling Vapor Recovery (ORVR) devices that recover refueling vaporsonboard the vehicle. Vapors produced as a result of dispensing fuel intoan ORVR equipped vehicle are collected onboard, and accordingly, are notavailable to flow through a vapor return passage to an AFS formeasurement. Thus, refueling an ORVR equipped vehicle results in apositive liquid fuel flow reading, but no return vapor flow reading(i.e. an AIL ratio equal to 0 or close thereto)—a condition thatnormally indicates vapor recovery malfunction. Because the vaporrecovery system cannot distinguish between ORVR equipped vehicles andconventional vehicles, the vapor recovery system may be falselydetermined to be malfunctioning when an ORVR equipped vehicle isrefueled.

[0017] In the coming years, 2000 to 2020 and beyond, the proportion ofORVR vehicles in use will increase. Therefore this problem will bebecome more severe in the coming decades. If A/L sensing is to be usedsuccessfully for vapor recovery system monitoring, then a method isneeded to distinguish between failed vapor recovery test events causedby an ORVR vapor-blocking vehicle and true failed vapor recovery testevents (which can only occur for non-ORVR equipped vehicles).

OBJECTS OF THE INVENTION

[0018] It is therefore an object of the present invention to provide amethod and system for determining acceptable performance of a vaporrecovery system in a fueling facility.

[0019] It is another object of the present invention to provide a methodand system for measuring the return flow of vapors from a dispensingpoint to a main fuel storage tank.

[0020] It is yet another object of the present invention to reduce thenumber of devices required to determine A/L ratios for individualdispensing points in a fueling facility.

[0021] It is still yet another object of the present invention toprovide a method and system for determining the integrity of vaporcontainment in a main fuel storage tank.

[0022] It is still a further object of the present invention to providea method and system for analyzing and indicating vapor recoveryperformance in a fueling facility.

[0023] It is still another object of the present invention to provide asystem and method for determining true vapor recovery system failures.

[0024] It is yet another object of the present invention to provide asystem and method for distinguishing between low A/L readings caused bya vapor recovery system failure and low A/L readings caused by thefueling of an ORVR-equipped vehicle.

[0025] Additional objects and advantages of the invention are set forth,in part, in the description which follows, and, in part, will beapparent to one of ordinary skill in the art from the description and/orfrom the practice of the invention.

SUMMARY OF THE INVENTION

[0026] In response to the foregoing challenges, applicants havedeveloped an innovative system for monitoring vapor recovery in a liquidfuel dispensing facility having at least one fuel dispensing pointconnected to a main fuel storage system by a means for supplying liquidfuel to the dispensing point and a means for returning vapor from thedispensing point, said monitoring system comprising: a vapor flow sensoroperatively connected to the means for returning vapor and adapted toindicate the amount of vapor flow through the means for returning vapor;a liquid fuel dispensing meter operatively connected to the means forsupplying liquid fuel and adapted to indicate the amount of liquid fueldispensed at the at least one fuel dispensing point; and a centralelectronic control and diagnostic arrangement having, a means fordetermining a ratio of vapor flow to dispensed liquid fuel for the atleast one fuel dispensing point, said determining means receivingdispensed liquid fuel amount information from the liquid fuel dispensingmeter and receiving vapor flow amount information from the vapor flowsensor, wherein the acceptability of vapor recovery for the fueldispensing point is determined by said ratio of vapor flow to dispensedliquid fuel.

[0027] Applicants have also developed an innovative system formonitoring vapor recovery in a liquid fuel dispensing facility having atleast two fuel dispensing points connected to a main fuel storage systemby a vapor return pipeline, said monitoring system comprising: a vaporflow sensor operatively connected to the vapor return pipeline; meansfor determining dispensed liquid fuel amount information for each fueldispensing point; and a means for determining a ratio of vapor flow todispensed liquid fuel for the fuel dispensing points based on vapor flowsensor readings and dispensed liquid fuel amount information, whereinthe acceptability of vapor recovery for the fuel dispensing points isdetermined by said ratio of vapor flow to dispensed liquid fuel.

[0028] Applicants have also developed an innovative method of monitoringvapor recovery in a liquid fuel dispensing facility having at least onefuel dispensing point connected to a main fuel storage system by a meansfor supplying liquid fuel to the dispensing point and a means forreturning vapors from the dispensing point, said monitoring methodcomprising the steps of: determining at multiple times an amount ofvapor flow through the means for returning vapors; determining atmultiple times an amount of liquid fuel dispensed through the means forsupplying liquid fuel; and determining a ratio of vapor flow todispensed liquid fuel for the fuel dispensing point based on the amountof vapor flow through the means for returning vapors and the amount ofliquid fuel dispensed through the means for supplying liquid fuel,wherein the acceptability of vapor recovery for the fuel dispensingpoint is determined by said ratio of vapor flow to dispensed liquidfuel.

[0029] Applicants have still further developed an innovative system formonitoring vapor containment in a liquid fuel dispensing facility havinga main fuel storage system connected by a vent pipe-pressure reliefvalve arrangement to atmosphere, said monitoring system comprising: apressure sensor operatively connected to the vent pipe; a vaporprocessor operatively connected to the vent pipe; and means fordetermining the acceptability of vapor containment in the main fuelstorage system, said determining means being operatively connected tothe pressure sensor to receive pressure level information therefrom andbeing operatively connected to the vapor processor to selectively causethe vapor processor to draw a negative pressure in the main fuel storagesystem.

[0030] Applicants have developed an innovative method of monitoringvapor containment in a liquid fuel dispensing facility having at leastone main fuel storage tank connected by a vent pipe-pressure reliefvalve arrangement to atmosphere, said monitoring method comprising thesteps of: identifying the start of an idle period for the liquid fueldispensing facility; monitoring the liquid fuel dispensing facility toconfirm maintenance of the idle period; determining whether pressure inthe main fuel storage tank is equal or below a minimum level;selectively adjusting pressure in the main fuel storage tank to a presetlower level when the previously determined pressure is above the minimumlevel; monitoring variation of the pressure in the main fuel storagetank during the remainder of the idle period; determining the end of theidle period; and determining the acceptability of vapor containment inthe main fuel storage tank based on the variation of the pressure duringthe idle period.

[0031] Applicants also developed an innovative method of determiningvapor recovery system failures associated with a single fuel dispensingpoint, said method comprising the steps of: determining the vapor flowto dispensed fuel ratios for a plurality of fuel dispensing points;determining the number of vapor flow to dispensed fuel ratios that arebelow a preset minimum for each of the plurality of fuel dispensingpoints; determining the average number of vapor flow to dispensed fuelratios below the preset minimum for the plurality of fuel dispensingpoints; and comparing the number vapor flow to dispensed fuel ratiosbelow the preset minimum for each of the plurality of fuel dispensingpoints to the average number of vapor flow to dispensed fuel ratiosbelow the present minimum to determine whether the vapor recovery systemassociated with each of the plurality of fuel dispensing points hasfailed.

[0032] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only, and are not restrictive of the invention as claimed.The accompanying drawings, which are incorporated herein by referenceand which constitute a part of this specification, illustrate certainembodiments of the invention, and together with the detailed descriptionserve to explain the principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention will be described in conjunction with the followingdrawings in which like reference numerals designate like elements andwherein:

[0034]FIG. 1 is a schematic view of a fueling system vapor recoveryperformance monitor in accordance with an embodiment of the presentinvention; and

[0035]FIG. 2 is a schematic view of a fueling system vapor recoveryperformance monitor in accordance with another embodiment of the presentinvention.

[0036]FIG. 3 is a graph used to convert vapor leakage rates based onullage pressures.

DETAILED DESCRIPTION OF THE INVENTION

[0037] A first embodiment of the invention is described in connectionwith FIG. 1, which shows a vapor recovery and containment monitoringsystem for use in a liquid fuel dispensing facility 10. The dispensingfacility 10 may include a station house 100, one or more fuel dispenserunits 200, a main fuel storage system 300, means for connecting thedispenser units to the main fuel storage system 400, and one or morevapor (or air) flow sensors (AFS's) 500.

[0038] The station house 100 may include a central electronic controland diagnostic arrangement 110 that includes a dispenser controller 120,dispenser current loop interface wiring 130 connecting the dispensercontroller 120 with the dispenser unit(s) 200, and a combined dataacquisition system/in-station diagnostic monitor 140. The dispensercontroller 120 may be electrically connected to the monitor 140 by afirst wiring bus 122. The interface wiring 130 may be electricallyconnected to the monitor 140 by a second wiring bus 132. The monitor 140may include standard computer storage and central processingcapabilities, keyboard input device(s), and audio and visual outputinterfaces among other conventional features.

[0039] The fuel dispenser units 200 may be provided in the form ofconventional “gas pumps.” Each fuel dispenser unit 200 may include oneor more fuel dispensing points typically defined by the nozzles 210. Thefuel dispenser units 200 may include one coaxial vapor/liquid splitter260, one vapor return passage 220, and one fuel supply passage 230 pernozzle 210. The vapor return passages 220 may be joined together beforeconnecting with a common vapor return pipe 410. The units 200 may alsoinclude one liquid fuel dispensing meter 240 per nozzle 210. The liquidfuel dispensing meters 240 may provide dispensed liquid fuel amountinformation to the dispenser controller 120 via the liquid fueldispensing meter interface 270 and interface wiring 130.

[0040] The main fuel storage system 300 may include one or more mainfuel storage tanks 310. It is appreciated that the storage tanks 310 maytypically be provided underground, however, underground placement of thetank is not required for application of the invention. It is alsoappreciated that the storage tank 310 shown in FIGS. 1 and 2 mayrepresent a grouping of multiple storage tanks tied together into astorage tank network. Each storage tank 310, or a grouping of storagetanks, may be connected to the atmosphere by a vent pipe 320. The ventpipe 320 may terminate in a pressure relief valve 330. A vapor processor340 may be connected to the vent pipe 320 intermediate of the storagetank 310 and the pressure relief valve 330. A pressure sensor 350 mayalso be operatively connected to the vent pipe 320. Alternately, it maybe connected directly to the storage tank 310 or the vapor return pipe410 below or near to the dispenser 200 since the pressure is normallysubstantially the same at all these points in the vapor containmentsystem. The storage tank 310 may also include an Automatic Tank GaugingSystem (ATGS) 360 used to provide information regarding the fuel levelin the storage tank. The vapor processor 340, the pressure sensor 350,and the automatic tank gauging system 360 may be electrically connectedto the monitor 140 by third, fourth, and fifth wiring busses 342, 352,and 362, respectively. The storage tank 310 may also include a fill pipeand fill tube 370 to provide a means to fill the tank with fuel and asubmersible pump 380 to supply the dispensers 200 with fuel from thestorage tank 310.

[0041] The means for connecting the dispenser units and the main fuelstorage system 400 may include one or more vapor return pipelines 410and one or more fuel supply pipelines 420. The vapor return pipelines410 and the fuel supply pipelines 420 are connected to the vapor returnpassages 220 and fuel supply passages 230, respectively, associated withmultiple fuel dispensing points 210. As such, a “vapor return pipeline”designates any return pipeline that carries the return vapor of two ormore vapor return passages 220.

[0042] The AFS 500 is operatively connected to a vapor return pipeline410. A basic premise of the system 10 is that it includes at most oneAFS 500 (also referred to more broadly as vapor flow sensors) for eachfuel dispenser unit 200. Thus, the AFS 500 must be operatively connectedto the vapor return system downstream of the vapor return passages 220.If such were not the case, the system would include one AFS 500 pernozzle 210 which violates the basic premise of the invention. Each AFS500 may be electrically connected to the monitor 140 by a sixth wiringbus 502.

[0043] In order to determine the acceptability of the performance ofvapor recovery in the facility 10, the ratio of vapor flow to dispensedliquid fuel is determined for each fuel dispensing point 210 included inthe facility. This ratio may be used to determine if the fuel dispensingpoint 210 in question is in fact recovering an equal volume of vapor foreach unit volume of liquid fuel dispensed by the dispensing point 210.

[0044] In the embodiment of the invention shown in FIG. 1, eachdispensing point 210 is served by an AFS 500 that is shared with atleast one other dispensing point 210. Mathematical data processing(described below) is used to determine an approximation of the vaporflow associated with each dispensing point 210. The amount of fueldispensed by each dispensing point 210 is known from the liquid fueldispensing meter 240 associated with each dispensing unit. Amount offuel (i.e. fuel volume) information may be transmitted from eachdispensing meter 240 to the dispenser controller 120 for use by themonitor 140. In an alternative embodiment of the invention, thedispensing meters 240 may be directly connected to the monitor 140 toprovide the amount of fuel information used to determine the A/L ratiofor each dispensing point 210.

[0045] Each AFS 500 measures multiple (at least two or more) dispensingpoint return vapor flows. In the embodiment of the invention shown inFIG. 1, a single AFS 500 measures all the dispensing point vapor flowsfor the facility 10. In the case of a single AFS per facility 10, theAFS is installed in the single common vapor return pipeline which runsbetween all the dispensers as a group, which are all tied together intoa common dispenser manifold pipe, and all the main fuel storage tanks asa group, which are all tied together in a common tank manifold pipe.Various groupings of combinations of feed dispensing point air flow'sper AFS are possible which fall between these two extremes described.

[0046] With reference to a second embodiment of the invention shown inFIG. 2, it is appreciated that multiple AFS's 500 could be deployed tomeasure various groupings of dispensing point 210 vapor flows, down to aminimum of only two dispensing point vapor flows. The latter example maybe realized by installing one AFS 500 in each dispenser housing 200,which typically contains two dispensing point's 210 (one dispensingpoint per dispenser side) or up to 6 dispensing points (hoses) inMulti-Product Dispensers (MPD's) (3 per side). The vapor flows pipedthrough the vapor return passage 220 may be tied together to feed thesingle AFS 500 in the dispenser housing.

[0047] As stated above, the monitor 140 may connect to the dispensercontroller 120, directly to the current loop interface wiring 130 ordirectly to the liquid fuel dispensing meter 240 to access the liquidfuel flow volume readings. The monitor 140 may also be connected to eachAFS 500 at the facility 10 so as to be supplied with vapor flow amount(i.e. vapor volume) information. The liquid fuel flow volume readingsare individualized fuel volume amounts associated with each dispensingpoint 210. The vapor flow volume readings are aggregate amountsresulting from various groupings of dispensing point 210 vapor flows,which therefore require mathematical analysis to separate or identifythe amounts attributable to the individual dispensing points 210. Thisanalysis may be accomplished by the monitor 140 which may includeprocessing means. Once the vapor flow information is determined for eachdispensing point 210, the A/L ratios for each dispensing point may bedetermined and a pass/fail determination may be made for each dispensingpoint based on the magnitude of the ratio. It is known that the ratiomay vary from 0 (bad) to around 1 (good), to a little greater than 1(which, depending upon the facility 10 design, can be either good orbad), to much greater than 1 (typically bad). This ratio information maybe provided to the facility operator via an audio signal and/or a visualsignal through the monitor 140. The ratio information may also result inthe automatic shut down of a dispensing point 210, or a recommendationfor dispensing point shut down.

[0048] The embodiments of the invention shown in FIGS. 1 and 2 mayprovide a significant improvement over known systems due to thereplacement of the multiple AFS's 500 (one per dispensing point,typically anywhere from 10 or 12 up to 30 or more per site) and theirassociated wiring with a single, or fewer AFS's 500 (about ½ as many orless, depending upon dispensing point groupings).

[0049] With reference to the embodiments of the invention shown in bothFIGS. 1 and 2, the mathematical analysis performed in the monitor 140 isdesigned to find correlations between aggregate vapor volume measuredduring AFS 500 ‘busy periods’ and individual dispensing point 210dispensed liquid fuel volume readings. The analysis is done separatelyfor each AFS 500 and it's associated dispensing point group (two or moredispensing point's). The end result is a set of estimated dispensingpoint A/L ratios, one ratio per dispensing point. After a group of AFS500 busy period data records are accumulated, a series of mathematicalsteps accomplish this beginning with a simple, 1-variable functionsolution and ending with more complex function solutions until allratios are determined. If a ratio can be determined in an earlier step,it is not necessary to estimate it in a subsequent step (it can be setas a constant in later steps to simplify computation of any remainingunknown ratios). The sequence of solvable function types are:

[0050] Type 1: A single linear function with one unknown for any AFSbusy records with only 1 active dispensing point.

[0051] Type 2: Two linear functions with two unknowns for any pair ofsimilar AFS busy records with 2 (identical) active dispensing point's(two simultaneous equations with two unknowns).

[0052] Type 3: Three or more linear functions each with two or moreunknowns for any remaining (unsolved) set of AFS busy records (at leastas many functions as unknowns).

[0053] Each AFS 500 busy period data record is formed after the AFSbecomes idle by recording the aggregate vapor volume, A, and theindividual metered liquid volumes, L_(m), where the subscript, m,denotes the dispensing point or meter number. This number ranges from 1to M total meters. Idle detection can be done by various means,including:

[0054] 1) the monitor 140 can track reported dispenser meter 240start/stop events from the dispenser controller 120, the dispensercurrent loop wiring 130, or directly from the liquid fuel dispensingmeter 240; or

[0055] 2) the Automatic Tank Gauging System 360 can provide main fuelstorage tank 310 liquid fuel levels to the monitor 140 for detection ofstatic level conditions (no ongoing dispensing) in all the storage tanks310.

[0056] The latter method (No. 2) can be used if it is desired that allAFS's 500 be idle prior to forming AFS busy data records. In the case ofa single AFS 500 per facility 10 (shown in FIG. 1), this method canalways be used.

[0057] The simple form of the relationship between A, L, and the A/Lratio, R, for an AFS busy record with one (1) active dispensing pointis: A=L_(m)R_(m)

[0058] so the simple solution for function type 1 is:

R _(m) =A/L _(m)

[0059] where R_(m) is the estimated A/L ratio for active dispensingpoint (meter), m.

[0060] In the more general case, each AFS busy period data record, n,has a measured aggregate vapor volume, A_(n), and the individual meteredliquid fuel volumes, L_(nm), where the first subscript, n, denotes thedata record number and the second subscript, m, denotes the dispensingpoint or meter number as before. The record number, n, ranges from 1 toN total records.

[0061] The generalized form of the relationship between A_(n), L_(nm),and R_(m) for multiple-dispensing point records is:

A _(n) =L _(n1) R ₁ +L _(n2) R ₂ +L _(n3) R ₃ + . . . +L _(nm) R _(m)

[0062] In the case of a pair of similar busy records with 2 activedispensing point's (same 2 dispensing point's in both records) therelationships are:

A ₁ =L ₁₁ R ₁ +L ₁₂ R ₂

A ₂ =L ₂₁ R ₁ +L ₂₂ R ₂

[0063] so the solutions for functions of type 2 are:$R_{1} = {{\frac{{A_{1}L_{22}} - {A_{2}L_{12}}}{{L_{11}L_{22}} - {L_{12}L_{21}}}\quad R_{2}} = \frac{{A_{2}L_{11}} - {A_{1}L_{21}}}{{L_{11}L_{22}} - {L_{12}L_{21}}}}$

[0064] Functions of type 3 can be solved as a least squares problemusing standard arithmetic.

[0065] Example record data set with subscript notation: n A_(n) L_(n1)L_(n2) L_(n3) etc. . . L_(nM) 1 18  0 12  6 etc. . .  0 2 33 10 15  0etc. . .  8 3 21  7  0  0 etc. . . 14 etc. . . N 18  0  0 18 etc. . .  0

[0066] For the entire data set, the matrix relationship is:$\begin{bmatrix}A_{1} \\A_{2} \\A_{3} \\\vdots \\A_{n}\end{bmatrix} = {{{\begin{bmatrix}L_{11} & L_{12} & \cdots & L_{1m} \\L_{21} & L_{22} & \cdots & L_{2m} \\L_{31} & L_{32} & \cdots & L_{3m} \\\vdots & \vdots & \vdots & \vdots \\L_{n1} & L_{n2} & \cdots & L_{n\quad m}\end{bmatrix}\begin{bmatrix}R_{1} \\R_{2} \\\vdots \\R_{m}\end{bmatrix}}\quad {or}\quad A} = {LR}}$

[0067] The solution for the ratio vector, R, is: R=(L ^(T) L)⁻¹ L ^(T) A

[0068] where the first term is the inverse of the transposed n x mmatrix, L, times itself which results in an m×m matrix, the middle termis the transposed matrix, L, which is an m×n matrix, and the last termis the vector A of length n, all of which results in the vector R, oflength m (one A/L ratio per meter).

[0069] This approach can provide good estimates of the true A/L ratios,even with excessive variability (noise) in the sensor readings. Morerecords result in better estimates for a given level of variability butthere must be at least as many records as unknowns for minimalperformance.

[0070] Dispensing point ratio solutions are based on the simplestfunction type possible. As a data set is processed and ratio solutionsare determined, they are in turn used to simplify solutions forremaining records in any record set. As an example, if two records existin a set, one of type 1 (a single active dispensing point busy period),and a second with two active dispensing points, one of which is the samedispensing point as in the first record, the first record is solveddirectly as a type 1 function and it's ratio result is used to simplifythe function for the second record. This produces a second type 1function.

[0071] Example records (2): n A_(n) L_(n1) L_(n2) 1 5 — 10 2 19.5 12 15

[0072] Initial functions:

A ₁ =L ₁₂ R ₂

5=10R ₂

A ₂ =L ₂₁ R ₁ +L ₂₂ R ₂

19.5=12R ₁+15R ₂

[0073] Solve first, substitute solution in second to simplify:$5 = { {10R_{2}}\Rightarrow R_{2}  = {\frac{5}{10} = 0.5}}$19.5 = 12R₁ + 15R₂ ⇒ 19.5 = 12R₁ + 15 * 0.5 = 12R₁ + 7.5

[0074] Solve second as a type 1 function:$19.5 = { {{12R_{1}} + 7.5}\Rightarrow 12  = { {12R_{1}}\Rightarrow R_{1}  = {\frac{12}{12} = 1.0}}}$

[0075] This simplification method is used at each step of the data setsolution process:

[0076] Step 1: Form simple (1-dispensing point) or generalized functionforms for each record.

[0077] Step 2: Solve all Type 1 functions.

[0078] Step 3: Substitute solutions from prior step into remaining setof functions.

[0079] Step 4: Reduce all functions to simpler forms and repeat fromstep 2.

[0080] Step 5: Find and solve any Type 2 function pairs.

[0081] Step 6: Substitute solutions from prior step into remaining setof functions.

[0082] Step 7: Reduce all functions to simpler forms and repeat fromstep 2.

[0083] Step 8: If possible, solve remaining functions as a Type 3 leastsquares problem.

[0084] Step 9: If step 8 is not possible, wait for more data records tosolve the remaining functions.

[0085] Alternatively, replace the 9-step sequence with steps 8 and 9alone. This approach has the benefit of always averaging or reducing theeffects of variability in the sensor readings.

[0086] The various embodiments of the invention discussed herein mayalso be used to detect vapor recovery equipment failures. Stage-II vaporrecovery equipment failures can have two distinct effects on patterns ofA/L ratios. The failures are determined by identifying these patterns inthe solved ratio set. The first type of failure involves a dispensingpoint nozzle 210, a hose 212, or vapor return passage 220 pathrestriction, or a vacuum assist pump failure which blocks or reducesair-vapor flow. The above solution methods may be used to identify thistype of failure by identification of one dispensing point with aconsistently lowered ratio.

[0087] The second type of failure that can occur involves a dispensingpoint 210 with a defective air valve which does not close properly toblock reverse vapor flow (i.e. out of the nozzle) when the dispensingpoint is idle. In such a case the ratio for the defective dispensingpoint will not be affected because when the dispensing point is active,the vapor flow is normal. However, when idle, vapors from other activedispensing points can be pushed past the defective air valve, out of theleaky dispensing point nozzle, and into the atmosphere. The activedispensing point(s) AFS 500 may or may not register the amount of lostvapor, depending upon whether the leaking dispensing point is part ofthe AFS group (won't register) or not (will register). If not, the idleAFS 500 will register reverse vapor flow. In that case, the leakingdispensing point can be detected by the reverse flow signal when itshould be idle.

[0088] Using the above solution methods described in connection with thefirst and second embodiments of the invention, when the leakingdispensing point is a member of the active AFS 500 group it results inlowered ratios for all dispensing points in the group except for theleaking dispensing point. Also, the lowered ratios vary depending uponthe number of active dispensing point's during each busy period. Whenmore (good) dispensing point's are active in an AFS 500 group, the lostvapor effect is shared in the solution, resulting in less depression ofthe individual ratios. Furthermore, if only part of the vapors escape tothe atmosphere, the effect is reduced, resulting in less depression ofthe individual ratios. Accordingly, a post-solution analysis may beconducted on the ratio patterns to determine the likely failure type,active dispensing point restriction or idle dispensing point leak.

[0089] A third embodiment of the invention concerns the use of a singlevapor pressure sensor 350 (same as CARB requirement) to activelydetermine the tightness of the overall vapor containing elements of thefacility including the fuel storage system 300, (which includes the ventpipe 320, pressure relief valve 330, etc.), the vapor return pipelines410, the vapor/liquid splitter 260, the vapor return passages 220, thedispenser hose 212, the nozzle 210, etc. The vapor pressure sensor 350may be connected anywhere in the fuel storage system 300 or the pipelinesystem 400, which includes but is not limited to the storage tank 310vapor-space, the common vapor return pipeline 410, or the storage tankvent pipe 320. The vapor pressure sensor 350 may be used periodically toactively measure the leakage of vapors from the overall system insteadof constantly measuring for leakage amount.

[0090] The method in accordance with the third embodiment of theinvention may be carried out as follows. The monitor 140 may beconnected to and access pressure readings from the vapor pressure sensor350. The monitor 140 controls the active test which is initiated bydetermining an idle period during which none of the dispensing units 200are in operation (similar to the A/L detection method using eitherdispensing meter events or ATGS tank levels). The idle condition may becontinuously monitored and the test aborted if any dispensing units gointo operation during the test. During the idle period the vaporpressure sensor 350 is used to determine the pressure in the system(i.e. the pressure in the storage tank 310). If the pressure is notadequately negative (vacuum) for the test, the vapor processor 340 maybe turned on to draw a negative pressure in the storage tank 310 as itprocesses vapors. If the vapor processor 340 is used, the monitor 140may be used to monitor the vapor pressure readings until they becomeadequately negative, typically −2 or −3 inches w.c. Once the vaporpressure is adequately negative, the vapor processor 340 may be turnedoff. Thereafter the vapor pressure sensor 350 readings may be monitoredduring the remaining idle time. If the system is adequately tight, thenegative pressure readings should hold or degrade only slowly. If thenegative pressure degrades too rapidly toward zero, the monitor 140 mayindicate that the system has failed the leakage test. A pass/failthreshold is used to make this determination. It can be set as apercentage of the initial negative pressure amount based on the desireddetection sensitivity and should be related to the amount of air inflowdetected relative to total storage tank 310 vapor space (ullage volume).

[0091] In an alternative of the third embodiment of the invention, asingle or multiple AFS's 500 located in the common or multiple vaporreturn pipeline(s) (same as A/L detection equipment) may be included toconduct an improved active test for system tightness. While a pressuresensor 350 alone suffices for conducting a tightness test, AFS 500readings can add to the amount of information available to augment testsensitivity and confirm the tightness condition or help locate thesource of a leak. Any air inflow from a leak point will register as flowon the AFS(s) 500. Flow and flow direction are a general indicator ofthe location of the source of incoming air (which dispensers and/ortanks/vents). Note that the AFS 500 readings are generally the moresensitive indicator of vapor recovery system tightness failure sincenegative pressure degradation is small due to the small amount of airinflow over seconds or minutes of time relative to the generally largestorage tank vapor-space volumes. For significant negative pressuredegradation, the amount of air inflow needs to be a significant portionof the storage tank vapor-space volume which can be in the thousands ortens of thousands of gallons.

[0092] The optional AFS(s) 500, and dispenser controller 120, dispensercurrent loop 130, or optional ATGS 360 are connected to the monitor 140which acquires and processes the data from the devices to conduct thetightness test and also controls (on/off) the vapor processor 340. Notethat only one vapor pressure sensor 350 is needed for multiple storagetanks 310 as long as they share a common vapor recovery system so thattheir vapor spaces are connected (piped) together.

[0093] In another alternative embodiment of the invention, the ATGS 360may not be required to conduct an active test for system tightness. Inthis case, the idle state of the vapor recovery system during which thetightness test is conducted must be determined by (lack of) fuelingmeter 240 activity and a precise estimation of leak rate is not possiblesince tank 310 vapor ullage space volume is not known. Instead a generalpass/fail indication can be provided when the pressure decays at apreset rate during a test period.

[0094] In yet another embodiment of the present invention, the systemsshown in FIGS. 1 and 2 may be used to conduct an improved passive vaporcontainment test. This test uses pressure in the vapor containingelements of the facility, barometric pressure, and ullage spacemeasurements to calculate the change in pressure over time for the vaporcontaining elements of the facility. This calculation, which is notusually based on data collected when the facility is operating at −2 to−3 inches w.c., may then be normalized to indicate leakage rates for afacility held at −2 to −3 inches w.c.

[0095] This passive method may be initiated by monitoring the pressureof the main fuel storage system 300 or any vapor containing element ofthe facility 10 between fuel dispensing periods with the pressure sensor350. Pressure data derived from sequential groupings of monitoredpressures and ullage determinations derived from the ATGS 360 readingsare recorded at periodic intervals by monitor 140. The derived recordeddata permits the determination of rate of change of pressure, Prate,versus time, t, obtained from a linear regression model:

p=p _(rate) ·t

[0096] within each interval, the main storage system 300 total ullagevolume, V_(ullage) represented by the sum of the individual storage tank310 ullage volumes, V_(ullage):

V _(ullage) =V _(ullage1) +V _(ullage2) + . . . +V _(ullageN) for tanks1 to N

[0097] where v_(ullage)=(tank capacity)−(volume of fuel in tank)obtained from the ATGS 360, and the average pressure, p_(avg) over eachinterval:

p_(avg)=(p ₁ +p ₂ + . . . +p _(N))/N for pressure samples 1 to N in theinterval

[0098] are recorded if the correlation to the linear model isacceptable, generally based on high correlation between pressure withrespect to time and the model.

[0099] Upon collection of a daily sample of such records, the product ofpressure rate and the total ullage volume, p_(rate)·V_(ullage), issorted by the associated average pressure, p_(avg), and grouped intoequally spaced average pressure ranges. A collection of averages of theproducts, (p_(rate)V_(ullage))_(avg), within each group:

(p _(rate) V _(ullage))_(avg)=((p _(rate) ·V _(ullage))₁+(p _(rate) ·V_(ullage))₂+ . . . +(p _(rate) ·V _(ullage))_(N))/N

[0100] for products 1 to N in each group and the midpoints of theaverage pressure ranges, p_(mid), within each group are used with alinear regression model to estimate the rate of change of pressure timesullage volume, P_(rate)V at a selected test pressure, p_(test), of, say,2 inches of water column, if the correlation to the linear model:

P _(rate) V=(P _(rate) V)_(slope) ·p _(test)

[0101] is acceptable generally based on high correlation between theaverage products, (p_(rate)V_(ullage))_(avg), with respect to midpointpressures, p_(mid), and the model. A typical graph of this model for atank system is shown in FIG. 3. It is noted that the curve must crossthe origin which indicates no rate of change of pressure, thus noleakage, when there is zero pressure drop across any leakage path, sincefor leakage to occur a pressure driving force is needed regardless ofullage volume.

[0102] The regression yields the slope coefficient, (P_(rate)V)_(slope),which is used to calculate the estimated pressure times ullage volume,P_(rate)V at a selected test pressure, p_(test), of, say, 2 inches ofwater column at which a leakage test failure rate can be defined,similar to the standard CARB TP-201.3 test procedure. In other words, ifthere is a leakage path and if the pressure in the ullage space of thetank system is set to 2″ wcg (water column gauge) (above ambientpressure), the tank will leak at the estimated rate, v_(rate), of

v _(rate) =P _(rate) V(p _(test))/p

[0103] where p is the absolute pressure in the tank ullage space,typically 410″ wca (water column absolute) (assuming ambient is 408″wca). This can be interpreted to mean that the rate of volume vapor lossfrom a leaking tank is equal to the proportional rate of change ofabsolute pressure times the total ullage volume. Note that p_(test) is agauge pressure (referenced to ambient) and p is an absolute pressure(referenced to a vacuum). This relationship is derived from the idealgas law, which governs the relationship between pressure, p, and volume,v, in an enclosed space at low pressures and temperatures:

p·v=n·R·T

[0104] where n is moles of gas, R is the universal gas constant, and Tis absolute temperature. Replacing n with mass per molecular weight(MW):

p·v=m·R·T/MW

[0105] Rearranging terms and replacing constant terms with k:

m=k·p where k=v·MW/(R·T)

[0106] Rate of mass loss due to a leak from an enclosed space is foundby forming the relationship of the difference between the ending andstarting mass divided by starting mass and the time period of the loss:

(m2−m1)/(m1·t)=(k·p2−k·p1)/(k·p1·t)

Δm/(m1·t)=(p2−p1)/(p1·t)

Δm/(m1·t)=Δp/(p1·t)

Δm/t=Δp·m1/(p1·t)

[0107] The last form describes the rate of mass loss as a function ofstarting mass times proportional pressure change rate over the testperiod. To find volume loss rate, relate mass and volume by massdensity, ρ:

ρ=m/v or m=ρ·v so m1=ρ1·v and mass loss: Δm=ρ·Δv

[0108] Substituting in above equation:

ρ·Δv/t=Δp·ρ1·v/(p1·t)

[0109] Assuming mass density does not change appreciably:

Δv/t=Δp·v/(p1·t) where ρ1≈ρ

[0110] Dropping the subscript and using notation for volume loss rate,v_(rate):

v _(rate) =Δp·v/(p·t)

[0111] which can be interpreted to mean that the volume loss rate is theproportional change of pressure times volume per unit time. But part ofthis expression is the calculated value derived from measurements in theabove section:

v _(rate) =P _(rate) V/p where v _(rate) =Δp·v/t at the selected testpressure, 2″ wcg

[0112] Using the above example, the volume leak rate, v_(rate), is:

v _(rate) =P _(rate) V/p=6000/410=14.6 CFH or cubic feet per hour at 2″wcg

[0113] As described above, in yet another embodiment of the invention,the system may also perform a method of distinguishing between truevapor recovery failure events and ORVR equipped vehicle refuelingevents. Identifying a false vapor recovery recovery system failure dueto refueling an ORVR-equipped vehicle may be accomplished by applyingstandard statistical concepts to a group of dispensing or refuelingevents from all the dispensing points 210 at a dispensing facility 10 toidentify true failed vapor collection dispensing points as opposed tofailed tests due to ORVR vapor-blocking activity.

[0114] There are two assumptions that may be made as a predicate todetermining true failed vapor collection: (1) that ORVR and non-ORVRactivity occurs somewhat randomly amongst all the dispensing points; and(2) that average ORVR activity does not reach 100% of all refuelingevents (a maximum of 80% can be assumed). Given these assumptions, agroup of vapor collection event A/L measurements taken from all thedispensing points 210 at a dispensing facility 10 may be used to makethe following determinations:

[0115] 1) Determine if the proportions of failed (close to zero A/L) andnon-failed events are statistically different at individual dispensingpoints relative to their expected proportions, due to the activity ofORVR vehicles, derived from all the dispensing points; and

[0116] 2) Determine if the proportion of the failed (close to zero)events at each dispensing point are statistically different from theproportion of the failed events derived from all the dispensing points,which are largely due to the effect of ORVR vehicles.

[0117] As a result of these determinations, the A/L ratio measurementsmay be used to test for blockage or leakage caused vapor recoveryfailure, with a mix of ORVR and non-ORVR vehicle activity.

[0118] On a regular (e.g. daily) basis, each dispensing point 210 mayhave a number of A/L determinations associated with it. It is presumedthat there are k dispensing points 210 and the i^(th) dispensing pointhas n_(i) A/L ratio determinations. Let X_(i) be the number of A/Ldeterminations for dispensing point I that indicate a “zero” or“blocked” A/L ratio. The assumption is that fueling an ORVR vehicle willresult in a zero or blocked A/L ratio. The total number of A/Ldeterminations for the site is:

n=Σn_(i)

[0119] and the total number of zero A/L ratios is:

X=ΣX_(i)

[0120] An overall test can be conducted to determine whether there areany significant differences in the proportion of A/L ratios indicatingblocked vapor flow among the dispensing points 210. This can beaccomplished using a chi-squared test on the table of data from the kdispensers: Veeder-Root Dispenser 1 Dispenser 2 Dispenser k Total NumberX1 X2 . . . Xk X blocked Not blocked n1-X1 n2-X2 . . . nk-Xk N-X Numbern1 n2 . . . nk N

[0121] The chi-squared statistic is given by:

X ²=Σ(O _(i) −E _(i))² /E _(i)

[0122] where O_(i) is the number observed in each cell of the table andE_(i) is the expected number in that cell. The data in the cellsindicate the number of A/L ratios that indicate a “blocked” conditionfor each dispensing point and the number of A/L ratios indicating a “notblocked” condition for that dispenser. The expected number “blocked”ratios for dispenser I is:

E _(i1) =n _(i)(X/N)

[0123] and the expected number of “not blocked” ratios for dispenser Iis:

n_(i)−E_(i)

[0124] The summation is carried out over 2k cells. This statistic iscompared to the critical value from a chi-squared table with k −1degrees of freedom. If it is significant, there is evidence that thedispensers have different proportions of blocked A/L ratios, so that oneor more would appear to be blocked on at least an intermittent basis.

[0125] In turn, an individual test can be performed for each dispenser.This tests whether each dispenser has a proportion of zero A/L ratiosthat exceeds the overall proportion for the station. The followingequation may be used to compute the overall proportion of zero A/Lratios for the period:

P=X/N

[0126] The following equation may be used to compute the proportion ofzero A/L ratios for each dispenser:

p _(i) =x _(i) /n _(i)

[0127] From the foregoing calculations, it may be concluded that thereis evidence that dispenser I is blocked if:

p _(i) >P+z _(α)(0.16/n _(i))^(½)

[0128] where z_(α) is the upper a percentage point from a standardnormal distribution. If a 1% significance level is desired, z_(α) is2.326, for example, (or 1.645 for a 5% significance level). The number0.16 in the formula results from assumption of the most conservativecase; that 80% of the vehicles are ORVR vehicles. Once a truly blockeddispensing point is detected, an audio or visual signal may be providedby the monitor 140 to indicate this condition. Truly blocked dispensingpoints may also be automatically shut down as a result of suchdetection.

[0129] It will be apparent to those skilled in the art that variousmodifications and variations may be made in the preparation andconfiguration of the present invention without departing from the scopeand spirit of the present invention. For example, various combinationsof the methods described above may be implemented without implementingthe full system shown FIGS. 1 and/or 2. Thus, it is intended that thepresent invention cover the modifications and variations of theinvention.

We claim:
 1. A system for monitoring vapor recovery in a liquid fueldispensing facility having at least one fuel dispensing point connectedto a main fuel storage system by a means for supplying liquid fuel tothe dispensing point and a means for returning vapor from the dispensingpoint, said monitoring system comprising: a vapor flow sensoroperatively connected to the means for returning vapor and adapted toindicate the amount of vapor flow through the means for returning vapor;a liquid fuel dispensing meter operatively connected to the means forsupplying liquid fuel and adapted to indicate the amount of liquid fueldispensed through the at least one fuel dispensing point; and a centralelectronic control and diagnostic arrangement having, a means fordetermining a ratio of vapor flow to dispensed liquid fuel for the atleast one fuel dispensing point, said determining means receivingdispensed liquid fuel amount information from the liquid fuel dispensingmeter and receiving vapor flow amount information from the vapor flowsensor, wherein the acceptability of vapor recovery for the fueldispensing point is determined by said ratio of vapor flow to dispensedliquid fuel.
 2. The monitoring system of claim 1 including at least twofuel dispensing points for each vapor flow sensor in the system.
 3. Themonitoring system of claim 1 wherein the means for returning vaporcomprises a vapor return pipeline, and wherein said vapor returnpipeline is operatively connected to the vapor flow sensor.
 4. Themonitoring system of claim 1 wherein the means for returning vaporcomprises one or more vapor return pipelines, and wherein each vaporreturn pipeline is connected to a plurality of vapor return passagesthat are connected to a respective plurality of fuel dispensing points.5. The monitoring system of claim 4 wherein each vapor return pipelineis operatively connected to a separate vapor flow sensor.
 6. Themonitoring system of claim 1 wherein the amount of vapor flow indicatesvapor volume.
 7. The monitoring system of claim 1 wherein the amount ofliquid fuel dispensed indicates liquid fuel volume.
 8. The monitoringsystem of claim 1 further comprising an automatic tank gauging systemoperatively connected to the central control and diagnostic arrangement.9. The monitoring system of claim 1 wherein the central control anddiagnostic arrangement further comprises means for determining the lossof vapor through the fuel dispensing point to atmosphere.
 10. Themonitoring system of claim 1 , further comprising means for monitoringvapor containment in the vapor containing elements of the liquid fueldispensing facility, said means for monitoring vapor containment beingoperatively connected to any vapor containing element of the liquid fueldispensing facility and the central electronic control and diagnosticarrangement.
 11. The monitoring system of claim 10 wherein the means formonitoring vapor containment includes: a vent pipe-pressure relief valvearrangement connecting one or more vapor containing elements of theliquid fuel dispensing facility to atmosphere; a pressure sensoroperatively connected to the vent pipe; a vapor processor operativelyconnected to the vent pipe; and means for determining the acceptabilityof vapor containment incorporated into the central electronic controland diagnostic arrangement, said means for determining acceptability ofvapor containment being operatively connected to the pressure sensor toreceive pressure level information therefrom and being operativelyconnected to the vapor processor to selectively cause the vaporprocessor to draw a negative pressure in the main fuel storage system.12. A system for monitoring vapor recovery in a liquid fuel dispensingfacility having at least two fuel dispensing points connected to a mainfuel storage system by a vapor return pipeline, said monitoring systemcomprising: a vapor flow sensor operatively connected to the vaporreturn pipeline; means for determining dispensed liquid fuel amountinformation for each fuel dispensing point; and a means for determininga ratio of vapor flow to dispensed liquid fuel for the fuel dispensingpoints based on vapor flow sensor readings and dispensed liquid fuelamount information, wherein the acceptability of vapor recovery for thefuel dispensing points is determined by said ratio of vapor flow todispensed liquid fuel.
 13. The monitoring system of claim 12 , furthercomprising means for monitoring vapor containment in the vaporcontaining elements of the liquid fuel dispensing facility, said meansfor monitoring vapor containment being operatively connected to anyvapor containing element of the liquid fuel dispensing facility.
 14. Amethod of monitoring vapor recovery in a liquid fuel dispensing facilityhaving at least one fuel dispensing point connected to a main fuelstorage system by a means for supplying liquid fuel to the dispensingpoint and a means for returning vapors from the dispensing point, saidmonitoring method comprising the steps of: determining at multiple timesan amount of vapor flow through the means for returning vapors;determining at multiple times an amount of liquid fuel dispensed throughthe means for supplying liquid fuel; and determining a ratio of vaporflow to dispensed liquid fuel for the fuel dispensing point based on theamount of vapor flow through the means for returning vapors and theamount of liquid fuel dispensed through the means for supplying liquidfuel, wherein the acceptability of vapor recovery for the fueldispensing point is determined by said ratio of vapor flow to dispensedliquid fuel.
 15. The method of claim 14 wherein the multiple times ofdetermining the amount of vapor flow and the multiple times ofdetermining the amount of liquid fuel dispensed correspond to eachother.
 16. The method of claim 14 wherein a ratio of vapor flow todispensed liquid fuel that is repeatedly determined to be less than 1for a dispensing point indicates a path restriction in an elementassociated with the dispensing point.
 17. The method of claim 14 whereina ratio of vapor flow to dispensed liquid fuel that is repeatedlydetermined to be greater than 1 for all dispensing points other than aselected dispensing point indicates that the selected dispensing pointleaks vapor to atmosphere during idle periods.
 18. The method of claim14 wherein the amount of vapor flow indicates vapor volume.
 19. Themethod of claim 14 wherein the amount of liquid fuel dispensed indicatesliquid fuel volume.
 20. The method of claim 14 further comprising thestep of determining the loss of vapor through the fuel dispensing pointto atmosphere.
 21. The method of claim 14 , wherein the liquid fueldispensing facility further comprises a vent pipe-pressure relief valvearrangement connecting the vapor containing elements of the facility toatmosphere, and further comprising the following steps of monitoringvapor containment in the vapor containing elements of the facility:identifying the start of an idle period for the liquid fuel dispensingfacility; monitoring the liquid fuel dispensing facility to confirmmaintenance of the idle period; determining whether pressure in at leastone of the vapor containing elements of the facility is equal to orbelow a minimum level; selectively adjusting pressure in the vaporcontaining elements of the facility to a preset lower level when thepreviously determined pressure is above the minimum level; monitoringvariation of the pressure in at least one of the vapor containingelements of the facility during the remainder of the idle period;determining the end of the idle period; and determining theacceptability of vapor containment in the vapor containing elements ofthe facility based on the variation of the pressure during the idleperiod.
 22. A system for monitoring vapor containment in a liquid fueldispensing facility having a main fuel storage system connected by avent pipe-pressure relief valve arrangement to atmosphere, saidmonitoring system comprising: a pressure sensor operatively connected tothe vent pipe; a vapor processor operatively connected to the vent pipe;and means for determining the acceptability of vapor containment in themain fuel storage system, said determining means being operativelyconnected to the pressure sensor to receive pressure level informationtherefrom and being operatively connected to the vapor processor toselectively cause the vapor processor to draw a negative pressure in themain fuel storage system.
 23. A method of monitoring vapor containmentin a liquid fuel dispensing facility having at least one main fuelstorage tank connected by a vent pipe-pressure relief valve arrangementto atmosphere, said monitoring method comprising the steps of:identifying the start of an idle period for the liquid fuel dispensingfacility; monitoring the liquid fuel dispensing facility to confirmmaintenance of the idle period; determining whether pressure in the mainfuel storage tank is equal or below a minimum level; selectivelyadjusting pressure in the main fuel storage tank to a preset lower levelwhen the previously determined pressure is above the minimum level;monitoring variation of the pressure in the main fuel storage tankduring the remainder of the idle period; determining the end of the idleperiod; and determining the acceptability of vapor containment in themain fuel storage tank based on the variation of the pressure during theidle period.
 24. The method of claim 23 wherein the minimum level is inthe range of −2 to −3 inches water column.
 25. The method of claim 23further comprising the step of monitoring vapor flow in a vaporcontaining elements of the facility during the idle period; anddetermining malfunctioning dispensing points based on vapor flowinformation.
 26. The method of claim 14 further comprising a method ofdetermining vapor recovery system failures associated with a single fueldispensing point, said method of determining vapor recovery systemfailures comprising the steps of: determining the vapor flow todispensed fuel ratios for a plurality of fuel dispensing points;determining the number of vapor flow to dispensed fuel ratios that arebelow a preset minimum for each of the plurality of fuel dispensingpoints; determining the average number of vapor flow to dispensed fuelratios below the preset minimum for the plurality of fuel dispensingpoints; and comparing the number of vapor flow to dispensed fuel ratiosbelow the preset minimum for each of the plurality of fuel dispensingpoints to the average number of vapor flow to dispensed fuel ratiosbelow the present minimum to determine whether the vapor recovery systemassociated with each of the plurality of fuel dispensing points hasfailed.
 27. The method of claim 21 further comprising the method ofdetermining vapor recovery system failures associated with a single fueldispensing point, said method of determining vapor recovery systemfailures comprising the steps of: determining the vapor flow todispensed fuel ratios for a plurality of fuel dispensing points;determining the number of vapor flow to dispensed fuel ratios that arebelow a preset minimum for each of the plurality of fuel dispensingpoints; determining the average number of vapor flow to dispensed fuelratios below the preset minimum for the plurality of fuel dispensingpoints; and comparing the number vapor flow to dispensed fuel ratiosbelow the preset minimum for each of the plurality of fuel dispensingpoints to the average number of vapor flow to dispensed fuel ratiosbelow the present minimum to determine whether the vapor recovery systemassociated with each of the plurality of fuel dispensing points hasfailed.
 28. The method of claim 14 further comprising the method ofdetermining vapor recovery system failures associated with a single fueldispensing point, said method of determining vapor recovery systemfailures comprising the steps of: determining the vapor flow todispensed fuel ratios for a plurality of fuel dispensing points;determining the number of vapor flow to dispensed fuel ratios that arebelow a preset minimum for each of the plurality of fuel dispensingpoints; determining the average number of vapor flow to dispensed fuelratios below the preset minimum for the plurality of fuel dispensingpoints; and comparing the number vapor flow to dispensed fuel ratiosbelow the preset minimum for each of the plurality of fuel dispensingpoints to the average number of vapor flow to dispensed fuel ratiosbelow the present minimum to determine whether the vapor recovery systemassociated with each of the plurality of fuel dispensing points hasfailed.
 29. A method of determining vapor recovery system failuresassociated with a single fuel dispensing point, said method comprisingthe steps of: determining the vapor flow to dispensed fuel ratios for aplurality of fuel dispensing points; determining the number of vaporflow to dispensed fuel ratios that are below a preset minimum for eachof the plurality of fuel dispensing points; determining the averagenumber of vapor flow to dispensed fuel ratios below the preset minimumfor the plurality of fuel dispensing points; and comparing the numbervapor flow to dispensed fuel ratios below the preset minimum for each ofthe plurality of fuel dispensing points to the average number of vaporflow to dispensed fuel ratios below the present minimum to determinewhether the vapor recovery system associated with each of the pluralityof fuel dispensing points has failed.